'use strict';

const fs = require('fs');
const path = require('path');
const paths = require('./paths');
const chalk = require('chalk');
const resolve = require('resolve');

/**
 * Get additional module paths based on the baseUrl of a compilerOptions object.
 * @param {Object} options
 */
function getAdditionalModulePaths(options = {}) {
  const baseUrl = options.baseUrl;

  // We need to explicitly check for null and undefined (and not a falsy value) because
  if (baseUrl == null) {
    //读取.env文件中设置的变量NODE_PATH
    const nodePath = process.env.NODE_PATH || 'src/';
    return nodePath.split(path.delimiter).filter(Boolean);
  }

  const baseUrlResolved = path.resolve(paths.appPath, baseUrl);

  // We don't need to do anything if `baseUrl` is set to `node_modules`. This is
  // the default behavior.
  if (path.relative(paths.appNodeModules, baseUrlResolved) === '') {
    return null;
  }

  // Allow the user set the `baseUrl` to `appSrc`.
  if (path.relative(paths.appSrc, baseUrlResolved) === '') {
    return [paths.appSrc];
  }

  // If the path is equal to the root directory we ignore it here.
  // We don't want to allow importing from the root directly as source files are
  // not transpiled outside of `src`. We do allow importing them with the
  // absolute path (e.g. `src/Components/Button.js`) but we set that up with
  // an alias.
  if (path.relative(paths.appPath, baseUrlResolved) === '') {
    return null;
  }

  // Otherwise, throw an error.
  throw new Error(
    chalk.red.bold(
      "Your project's `baseUrl` can only be set to `src` or `node_modules`." +
      ' Create React App does not support other values at this time.'
    )
  );
}

/**
 * 设置目录别名
 */
function getWebpackAliases(options = {}) {
  const baseUrl = options.baseUrl ? options.baseUrl : '/src';

  const baseUrlResolved = path.resolve(paths.appPath, baseUrl);

  if (path.relative(paths.appPath, baseUrlResolved) === '') {
    return {
      src: paths.appSrc,
    };
  }
}

function getModules() {
  //判断jsconfig.json配置文件是否存在
  const hasJsConfig = fs.existsSync(paths.appJsConfig);
  let config;
  if (hasJsConfig) {
    //获取json配置文件的内容
    config = require(paths.appJsConfig);
  }
  config = config || {};
  const options = config.compilerOptions || {};
  const additionalModulePaths = getAdditionalModulePaths(options);
  //设置alias（目录别名）
  return {
    additionalModulePaths: additionalModulePaths,
    webpackAliases: getWebpackAliases(options)
  };
}

module.exports = getModules();